FIG. 1 shows a frame structure of a TDD (Time Division Duplex) mode in an LTE (Long Term Evolution) system. In this frame structure, one radio frame of 10 ms is divided into two half-frames. Every half-frame is divided into 10 time slots (number from 0 to 9) with a length of 0.5 ms respectively, and two time slots constitute one subframe with a length of 1 ms. One half-frame consists of 5 subframes (number from 0 to 4). For short cyclic prefixes which are 5.21 us and 4.69 us in length, one time slot consists of 7 symbols with a length of 66.7 us, wherein the cyclic prefix (CP) of the first symbol is 5.21 us in length, the cyclic prefixes of the other 6 symbols are 4.69 us in length; for a long CP which is 16.67 us in length, one time slot consists of 6 symbols. In this frame structure, the configuration characteristics of the subframe are shown as follows:
(1) subframe 0 is fixedly used for a downlink;
(2) subframe 1 (called special subframe thereinafter) consists of 3 special time slots: a DwPTS (Downlink Pilot Time Slot), a GP (Guard Period) and a UpPTS (Uplink Pilot Time Slot) respectively, wherein:
1) the DwPTS is used for the downlink, and at least one symbol is used for transmitting a P-SCH (Primary Synchronization Channel); when the DwPTS consists of a plurality of symbols, the P-SCH is placed in the first symbol (as shown in FIG. 1);
2) the GP is guard time, without transmitting any data; and
3) the UpPTS is used for an uplink, and it may be used for transmitting signals such as an RACH (Random Access Channel), data, sounding pilot etc; and
(3) the former n subframe(s) after subframe 1 may be used for uplink transmitting (1≦n≦3), and the latter 3−n subframe(s) may be used for downlink transmitting.
As shown in FIG. 2, the RACH channel consists of the CP and a preamble, which are Tcp and Tpre in length respectively. The CP may be 0. Moreover, the distance between the end position of the preamble and the end position of the UpPTS is Tgt (as shown in FIG. 1). In certain standards, the CP and the preamble are generally called preamble. The CP is still called cyclic prefix, and the preamble shown in FIG. 2 is called sequence. The names of the RACH channel structure and its components in the present invention are according to FIG. 2.
With respect on how to transmit a signal on the RACH in the UpPTS, the corresponding solutions of the structure and transmitting method have not yet been proposed until now.